It is desirable that the beads can each easily be brought to the correct position with respect to the building drum and that not only they are correctly retained in that position, but that also the apex and flipper pertaining to the bead are laterally supported, i.e. in a direction parallel to the centre line of the building drum. Furthermore it is desirable that the finished product can easily be removed from the building drum.
A so-called "flat" building drum, meaning that it is substantially cylindrical in its passive position and that it therefore substantially lacks any radially protruding parts, is already known, both for easily achieving the correct positioning as referred to above and for easy removal, also referred to above. In order to correctly secure the beads in the manner mentioned above, this "flat" building drum comprises pressure segments that in their radially expanded condition carry and clamp the beads and which in their retracted condition provide the desired easy supply to and discharge off the building drum.
Apart from that, it is known to have means which are radially expandable from the building drum in order to provide the above-mentioned lateral support of the bead. However, particularly with radial tires for passenger cars the height of the apex and flipper pertaining to the bead may amount to at least four times the thickness of the bead wire bundle. Therefore it is necessary that the support means can be expanded to a sufficient height so as to laterally support also the apex and flipper, said means being retractable again.